This invention relates to flight instruments and more particularly to flight instruments based on light interference phenomena for sensing air pressure.
There are, in most aircraft, a group of flight instruments that are based on the principle of detecting pressure changes, especially the atmospheric air pressure. The instruments are: (a) the airspeed indicator which senses the difference between the air pressure on the inlet of a pitot tube placed at the front of the aircraft and the reference pressure at some pressure-neutral point of the aircraft fuselage, and (b): the altimeter which measures the aircraft altitude as a function of the barometric pressure at the altitude of the aircraft and (c): the rate-of-climb indicator which measures the rate-of-climb or descent of the aircraft by measuring the difference between the air pressure in a plenum containing a volume of air and connected through a restriction to the point of reference pressure and the unrestricted reference air pressure. In other words, the rate-of-climb indicator performs a differentiation of the air pressure as a function of the aircraft's changing altitude.
The three instruments listed hereinabove all contain an air pressure sensing device which is typically a diaphragm exposed on one or both sides to the air pressure to be measured. The diaphragm is, in conventional flight instruments, connected through a sensitive mechanical linkage to a rotating pointer in front of a dial which displays the visual indication provided by the instrument, such as air speed in nautical miles per hour, altitude in feet and thousands of feet and rate-of-climb in feet per second.
Another flight instrument which depends on sensing of pressures is the accelerometer, which is part of the inertial guidance system used in some large aircraft for navigation. The accelerometer senses the pressure changes as a force exerted on a mass in the accelerometer as the aircraft undergoes changes in velocity. This force is usually sensed by means of suitable electronic sensors that are part of the accelerometer.
The instant application discloses methods for the use of light interference phenomena, which are created by a beam of coherent monochromatic light, for sensing of pressures in flight instruments with a high degree of precision.
Flight instruments of conventional construction based on bellows action or mechanical linkages are subject to corrosion, mechanical wear and intrusion of dust which all contribute to loss of dependability and accuracy.